CoMP transmission/reception has been considered as a promising technology by 3GPP (3rd Generation Partnership Project) LTE-A (Long Term Evolution-Advanced) due to its potential to improve coverage, cell-edge throughput, and/or spectrum efficiency transmission. Since coordinated scheduling/beamforming (CS/CB) does not require data sharing among multiple transmission points (TPs), it has become the most feasible implementation scheme for CoMP in the case of X2-based multiple eNBs (evolved Node Bases) coordination. In CB, the transmit-side precoding applied to downlink transmissions is coordinated between TPs in order to reduce interference between the coverage areas of different TPs. In CS, transmission powers and resource allocations are coordinated in order to reduce interference.
Typically, CS/CB requires tight coordinated and synchronized decisions among eNBs within a cooperating cluster. However, for a realistic network, backhauls are not ideal and typically have approximately 15 to 60 ms delays. Such delays may impact the coordination efficiency of CS/CB, and lead to great design challenges for CS/CB.
Given the above, the X2 interface used for exchanging signaling information between eNBs should provide robust information with respect to the delay and be capable of assisting each eNB to make proper decisions and benefit the whole network with synergy. Therefore, an enhanced X2 signaling is required.